Evaluating Water Quality. Abiotic and Biotic Factors. What is water quality?. Appearance of the water Ability for humans to drink and use the water Clean enough for organisms that live in the water. Abiotic Factors. Certain abiotic factors affect water quality. For example:
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Abiotic and Biotic Factors
Certain abiotic factors affect water quality. For example:
For each factor, make sure you know :
The pH scale measures whether a substance is acidic or basic (alcaline)
pH 1 : a strong acid (like car battery acid or your stomach acid)
pH 6 : a weak acid (like milk)
pH 7 : neutral – neither acidic nor basic (like distilled water)
pH 8 : a weak base (like baking soda or human blood)
pH 14 : a strong base (like oven cleaner or drain cleaner)
Normal level in freshwater systems in Newfoundland and Labrador – about pH 6-6,5
Acceptable level for most aquatic organisms - between pH 5 - 8.5 (depending on the organism)
If the water is too acidic, some organisms can’t tolerate the conditions (do you remember range of tolerance from Grade 7?)
We measure pH with a probe, or with a
universal indicator (such as in pH paper)
that changes colour to show the pH
according to a scale
If there are too many non-dissolved solids in suspension, the water is turbid.
Normal level: little or no non-dissolved solids
How to measure :
a. Relative scale
Use a subjective scale from 1 to 5 - 1 is very clear and 5 is very turbid/opaque
b. Secchi disc
Use a black and white disk and lower it into the water. The deeper the disk can be seen, the more clear (less turbid) the water.
ecchi disc being lowered into the water →
Phosphates are a chemical compound that always include the elements phosphorus and oxygen. They are found in fertilizers and some detergents. They are an essential nutrient for plants.
Less than 0.1 mg/L (0.1 ppm)
But, if levels are too high, phosphates can cause an overproduction of plants, algae in particular (this is called eutrophication)
Eutrophication – overgrowth of algae:
This causes turbidity (look back at the consequences of that). As well, bacteria feeding on all the decomposing algae consume lots of dissolved oxygen, so other oragnisms don’t have enough
Can you remember the definition from last year?
Normal temperature of freshwater systems in Newfoundland and Labrador is between 0ºC and 18ºC
Water temperature is, unsurprisingly, measured with a thermometer
4. Dissolved oxygen
Dissolved oxygen refers to the quantity of oxygen in solution in water. It can be affected by abiotic and biotic factors.
Abiotic factors that affect dissolved oxygen:
Biotic factors that affect dissolved oxygen
Most aquatic organisms need at least 5 mg/L (= 5 ppm) of dissolved oxygen to survive – especially larger organisms such as fish.
If there isn’t enough dissolved oxygen in the water, organisms can’t survive.
How to measure :
1. Biological indicators
Some organisms can tell us something about water quality. Note: biological indicators don’t AFFECT water quality; they are AFFECTED BY the water quality.
Normally, the wider the variety of insects and other aquatic invertebrates, the cleaner the water.
If we only find leeches, worms and midge larvae, the water is probably not of good quality.